1. Field of the Invention
The present invention relates to a liquid crystal display device, having a touch sensor function, in which one of two sensor electrodes is disposed across a liquid crystal enclosed between first and second substrates from the other thereof, and a method of manufacturing the same.
2. Description of the Related Art
A liquid crystal display device has advantages such as thinning, weight saving, and low power consumption. For this reason, the liquid crystal display device is applied to a large number of electronic apparatuses for mobile applications such as a mobile phone and a digital camera.
The liquid crystal display device has a liquid crystal panel in which a liquid crystal is enclosed between a pair of substrates. In the liquid crystal display device, a light radiated from a planar surface light source such as a backlight provided on a back surface of the liquid crystal panel is modulated by the liquid crystal panel. Also, the display of an image is carried out on a front surface (a side of viewing a display surface) of the liquid crystal panel by the modulated light.
In recent years, a liquid crystal display device having a sensor function called “a touch panel” with which data representing contents instructed by a user is directly inputted by utilizing an icon or the like displayed on a screen of the liquid crystal display device has been realized.
The touch panel is installed on the display surface side of the liquid crystal display device so that the instructed contents shown on the screen of the liquid crystal display device can be selected with a hand of a human being or an object (for example, a stylus pen). When the hand of the human being or the object directly touches the touch panel, the touch panel detects a position within the panel surface which the hand of the human being or the object touches. The liquid crystal display device receives the instructed contents in the form of an input signal in accordance with the position where the contact is detected, and carries out an operation based on the input signal.
When the liquid crystal display device including the touch panel is used in a computer or the like, there is no need for providing an input unit as an attached accessory, outside a main body and a display device, such as a keyboard or a mouse. Alternatively, the touch panel provides another input unit which assists such an input unit. In addition, when the touch panel is used in a mobile product such as a mobile phone, there is no need for providing an input unit such as a keypad, or the number of keys is reduced.
From the above, when the touch panel is mounted to the liquid crystal display device, the number of special attached accessories is reduced. For the product provider side, when the number of attached accessories is less, there is provided an advantage that the degree of freedom of the product design increases, and thus the miniaturization and the convenience enhancement are progressed, thereby increasing the product power. This provides the advantages such as the price-reduction, high functionality and convenience enhancement of the product for the user side as well. For this reason, the use of the touch panel has a tendency to increase yearly.
A liquid crystal display device in which a touch panel is added to a display surface side of a liquid crystal display panel is known in terms of a method of mounting the touch panel.
However, it is disadvantageous to the thinning of the display device that the touch panel is externally added, which becomes a primary factor of an increase in manufacturing cost. In addition, in the liquid crystal display device to which the touch panel is externally added, the optical characteristics in a phase of image display changes due to an influence of a refractive interface, so that the visibility of the image is reduced. For this reason, it is studied that the liquid crystal display panel and the touch panel are formed integrally with each other.
A resistance film system, an electrostatic capacitance system, and an optical system are known as a detection system in the touch panel. Of these systems, in the touch panel utilizing the resistance film system, one point detection is a principle. Thus, the use of the application of the touch panel utilizing the resistance film system is limited.
It is studied in the systems to form the liquid crystal display panel and the touch panel integrally with each other.
In particular, when the liquid crystal display panel and the touch panel are formed integrally with each other in the resistance film system, a pixel array drive wiring for display can be effectively used as a wiring as well for detection of a change in resistance. Therefore, the resolution for display is prevented from being reduced, and the precision of position detection by a sensor is high. Also, an additional function such as a multi-point detecting function can be obtained.
There is known a liquid crystal display device, with a touch sensor, in which paired electrodes (hereinafter referred to as either “first and second sensor electrodes” or “touch electrodes”) which contact each other when the user presses a panel surface with his/her finger or the like are formed on two substrates, respectively, through which a liquid crystal layer is sandwiched for the purpose of forming the liquid crystal display panel and the touch panel integrally with each other in the resistance film system. This liquid crystal display device, for example, is described in Japanese Patent Laid-open No. 2001-75074.
In the liquid crystal display device having the touch sensor function utilizing the resistance film system and having the structure as described above, the two sensor electrodes need to be formed contactably each other so as to hold the liquid crystal layer between the two sensor electrodes.
In general, however, the liquid crystal layer is located so as to contact an alignment film for determining an alignment direction of a liquid crystal molecule. For this reason, in order to apply the structure described above, the first and second sensor electrodes are obliged to contact the alignment film with the alignment film being held between the first and second sensor electrodes. For this reason, since a part of the alignment film which the first and second sensor electrodes contact is shaved, and as a result, there is a possibility that the imperfect alignment is caused, or the alignment film shaved floats in the liquid crystal to cause the imperfect display. Therefore, in the liquid crystal display device, utilizing the resistance film system, having such a structure, it is feared from the reason described above that the display grade can not be maintained by repetitively using the touch sensor.
There is known a liquid crystal display devices, having the touch sensor function utilizing the resistance film system, in which in order to avoid such inconvenience, a portion of an alignment film which sensor electrodes contact is removed. This liquid crystal display devices, for example, is described in Japanese Patent Laid-open No. 2007-52368.